Disclosure statement

Cameron Webb and the Department of Medical Entomology, NSW Health Pathology and University of Sydney, have been engaged by a wide range of insect repellent and insecticide manufacturers to provide testing of products and provide expert advice on mosquito biology. Cameron has also received funding from local, state and federal agencies to undertake research into mosquito-borne disease surveillance and management.

Andrew van den Hurk has received funding from local, state and federal agencies to study the ecology of mosquito-borne pathogens, and their surveillance and control. He is an employee of the Department of Health, Queensland Government.

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If you’re travelling to Asia, you’re probably mindful of the risks of malaria, dengue, or Zika. But authorities are warning Australians to take care to avoid another mosquito-borne disease, Japanese encephalitis, when holidaying in the region, after a spike in cases in Indonesia.

Japanese encephalitic virus is part of the flavivirus family, which is also responsible for Zika, dengue and yellow fever.

Most people infected don’t suffer any symptoms. But around 1% of cases will result in severe illness. Symptoms include fever, headache and vomiting, which can progress to neurological complications, such as disorientation, seizures, and paralysis.

Of those who do suffer severe illness, almost one-third will die; while up to half of those who survive are left with long-term neurological impairment.

There is no specific treatment for the disease, but it can be prevented with a vaccine.

How does it spread?

The virus is maintained in nature between mosquitoes and waterbirds, mainly herons and egrets. Pigs are also an important host, especially when they’re kept close to both people and sources of mosquitoes, such as rice paddies or other agricultural areas that use flood irrigation. Outbreaks are also more likely to occur during the monsoon season.

The mosquitoes that spread Japanese encephalitis virus are different to Aedes aegypti and Aedes albopictus – the mosquitoes that spread dengue, yellow fever and Zika viruses. These mosquitoes are active during the day and closely associated with small water-holding containers in urban areas.

The mosquitoes that transmit Japanese encephalitis virus, especially those belonging to the genus Culex, are usually found in wetlands and drainage ditches, and will be out biting mostly at dawn and dusk.

The Culex group of mosquitoes plays an important role in spreading Japanese encephalitis virus.Stephen Doggett (NSW Health Pathology)

Is Australia at risk?

Given outbreaks of Japanese encephalitis virus have occurred in Torres Strait and neighbouring Papua New Guinea, concern has been raised about the potential introduction and spread of the virus in Australia.

Perhaps our local flaviviruses provide some immunity in local wildlife to infection with Japanese encephalitis virus. Research has shown that local mosquitoes may be more likely to bite local native wildlife (such as wallabies) than pigs, providing some protection for Australia from local outbreaks.

While the risk of a local outbreak is low, Australian travellers should not be complacent.

How can Australian travellers stay safe?

There is a vaccine for Japanese encephalitis, but few travellers choose to have it, as they’re often told the risks are low unless they’re spending extensive time in rural or high-risk areas.

There is less than a one in a million chance you may be infected during travel to a country that experiences regular outbreaks of the disease. But short trips aren’t entirely risk-free; travellers to Asia still need to take suitable precautions.

A study investigating 55 cases of international travellers becoming infected with Japanese encephalitis virus indicated that most spent over a month at their destination but very few were vaccinated against the virus.

Rice paddies can be a breeding ground for mosquitoes that spread Japanese encephalitis virus throughout Asia.From Flickr user sinta1

The reality is there is a far greater risk that you’ll be infected by dengue while travelling in southeast Asia than Japanese encephalitis virus. But in recent years, Australian travellers have been infected with Japanese encephalitis virus in Thailand and Bali.

If you’re venturing out of holiday resorts to rural areas, consider vaccination as well. Even if you’re not, you can still get vaccinated before you go, but discuss this with your local doctor as part of your pre-travel health checks.

It only takes a single bite from an infected mosquito to transmit Japanese encephalitis virus and sometimes you can be in the wrong place at the wrong time.